U.S. patent number 6,579,418 [Application Number 09/899,314] was granted by the patent office on 2003-06-17 for leakage control system for treatment of moving webs.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Frank Stephen Hada, Michael Alan Hermans, Jeffrey Dean Lindsay.
United States Patent |
6,579,418 |
Lindsay , et al. |
June 17, 2003 |
Leakage control system for treatment of moving webs
Abstract
Pressurized web treatment systems include a moving web that
passes through a pressurized treatment chamber having a sealing
assembly with a leakage control system. Leakage control is achieved
by the cooperative effect of localized leak detectors and leak
reduction means that applies a local sealing force on the seal
assembly responsive to a signal from the leak detectors such that
increased sealing occurs in the vicinity of the leak. In
particular, an air press for paper web dewatering has improved
efficiency by virtue of the leakage control system, which features
local leak detectors and local force generation means associated
with a flexible seal assembly to reduce leakage at the edges of the
stationary plenum of the air press. Local leak detection can be
based on sonic measurement with microphones, detection of escaping
tracer gas, optical signals, and other means. Other embodiments of
web treatment systems include those for continuous production of
activated carbon fabrics and steam and chemical treatment of
textiles and other fibrous webs.
Inventors: |
Lindsay; Jeffrey Dean
(Appleton, WI), Hermans; Michael Alan (Neenah, WI), Hada;
Frank Stephen (Appleton, WI) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
|
Family
ID: |
22456843 |
Appl.
No.: |
09/899,314 |
Filed: |
July 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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133064 |
Aug 12, 1998 |
6280573 |
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Current U.S.
Class: |
162/198; 162/252;
162/262; 162/263; 34/405; 422/295; 8/101; 8/115.51; 422/297;
422/292; 34/242 |
Current CPC
Class: |
D21F
5/18 (20130101); D21F 3/0272 (20130101); D21F
1/48 (20130101) |
Current International
Class: |
D21F
3/02 (20060101); D21F 1/48 (20060101); D21F
5/00 (20060101); D21F 5/18 (20060101); D21F
003/00 (); F26B 025/00 () |
Field of
Search: |
;162/198,199,252,262,263
;34/242,405 ;73/40 ;422/292,295,297 ;8/101,115.51 |
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|
Primary Examiner: Chin; Peter
Attorney, Agent or Firm: Charlier; Patricia A. Gage; Thomas
M.
Parent Case Text
This application is a continuation of application Ser. No.
09/133,064 entitled LEAKAGE CONTROL SYSTEM FOR TREATMENT OF MOVING
WEBS and filed in the U.S. Patent and Trademark Office on Aug. 12,
1998 now U.S. Pat. No. 6,280,573. The entirety of application Ser.
No. 09/133,064 is hereby incorporated by reference.
Claims
We claim:
1. A control system for detecting and reducing fluid leaks along a
seal between a moving fabric web and a web treatment chamber,
wherein the web treatment chamber comprises a plenum for applying a
fluid at a pressure other than the ambient pressure to a surface of
the moving fabric web to directly contact the moving fabric web,
and a seal between the plenum and the moving fabric web, the
control system comprising: (a) a leak detector mounted near the
seal, adapted to produce a signal to indicate the presence and
location of a fluid leak between the moving fabric web and the
seal; and (b) localized leak reduction means responsive to the
signal produced by the leak detector.
2. The control system of claim 1, wherein the leak detector
comprises acoustic sensors.
3. The control system of claim 1, wherein the leak reduction means
comprises a multiplicity of sealing elements which apply variable
sealing pressure to the seal.
4. The control system of claim 1, wherein the leak reduction means
comprises a force distribution actuator which applies locally
variable force to the seal.
5. The control system of claim 1, wherein the leak detector
produces an electrical signal and the leak reduction means responds
to the electrical signal.
6. The control system of claim 1, wherein the web treatment chamber
applies a reactive chemical to the moving fabric web.
7. The control system of claim 1, wherein the web treatment chamber
further comprises an opposing chamber for removing the applied
fluid from the plenum, wherein the plenum is in a facing,
cooperative relationship with the opposing chamber disposed such
that the moving fabric web passes between the plenum and the
opposing chamber.
8. The control system of claim 7, wherein the opposing chamber is a
vacuum box.
9. The control system of claim 1, wherein the moving fabric web is
a nonwoven web.
10. The control system of claim 1, wherein the localized leak
reduction means comprises a force generator for adjusting local
sealing force on the seal.
11. The control system of claim 10, wherein the force generator is
selected from thermal expanding rods, thermal expanding beam
elements, thermal hydraulic actuators, mechanical actuators,
motors, piezoelectric elements, air bags, air hoses, gas cylinders,
pneumatic pistons, hydraulic pistons, thermoelectric actuators,
mechanical screws, gear assemblies, pulley assemblies, lever and
fulcrum assemblies, adjustable spring assemblies, screw and jack
assemblies, and magnetic force generation systems.
12. The control system of claim 1, wherein the plenum is at a
pressure lower than atmospheric pressure.
13. The control system of claim 1, wherein the plenum is at a
pressure greater than atmospheric pressure.
14. The control system of claim 1, having a Local Sensitivity of 20
or less.
15. A method for reducing leaks in a pressurized web treatment
system for treating a moving fabric web with a pressurized fluid,
the web treatment system comprising a pressurized chamber, a seal
between the moving fabric web and the pressurized chamber, a leak
detector positioned near the seal, and means for removing the
pressurized fluid from the web treatment system, the method
comprising: (a) detecting a leak along the seal with the leak
detector; (b) identifying the approximate location of the leak; (c)
generating a signal indicative of the approximate location of the
leak; and (d) increasing local sealing pressure above a
predetermined minimum along the seal in the approximate location of
the leak responsive to the signal.
16. The method of claim 15, further comprising incrementally
reducing the local sealing pressure in the region where sealing
pressure was previously increased until leakage in said region
begins to increase, then increasing the sealing pressure again
slightly to a level before increased leakage was detected, whereby
excessive sealing pressures are avoided.
17. A pressurized web treatment system for applying a pressurized
fluid from a fluid source to a moving fabric web while dynamically
reducing fluid leaks to the atmosphere, comprising: (a) a web
treatment chamber comprising chamber walls that define an interior
plenum, a fluid inlet for receiving pressurized fluid from a fluid
source, an opening for applying pressurized fluid to a moving
fabric web, a leading edge and a trailing edge both extending in
the cross direction, opposing side edges extending in the machine
direction, and a flexible seal assembly along at least one of the
leading edge, the trailing edge, and the side edges, the seal
assembly comprising a first seal head in contact with the web
treatment chamber and an opposing second seal head with the moving
fabric web passing between the first and second seal heads and
wherein one of the first and second seal heads is urged toward the
other of the first and second seal heads with a sealing force, and
means for removing the applied fluid from the web treatment
chamber; and (b) a control system for reducing fluid leaks along
the seal assembly comprising a leak detector for identifying the
presence and location of a fluid leak between the moving fabric web
and the seal assembly, and localized leak reduction means
responsive to the leak detector, wherein the localized leak
reduction means comprises a force generator for variably adjusting
the sealing pressure along the length of the seal assembly to
reduce leakage in the vicinity of the fluid leak as identified by
the leak detector.
18. A treatment system for a moving fabric web having a first
surface and a second surface, comprising: (a) a chamber comprising
a plenum for pressurized fluid in fluid communication with the
moving fabric web, the chamber having at least one edge along which
the moving fabric web travels into or out of the chamber; (b) a
flexible seal assembly in contact with said at least one edge for
preventing leakage of pressurized fluid from the treatment system;
(c) a leak detector responsive to fluid leaks along the seal
assembly such that the approximate location of fluid leaks can be
identified; (d) localized leak reduction means along the seal
assembly cooperatively associated with the leak detector such that
increased sealing force is applied where leaks occur; and (e) means
for removing the applied fluid from the web treatment system.
19. The treatment system of claim 18 wherein the leak reduction
means has a Local Sensitivity of three or greater.
20. The control system of claim 18, having a Local Sensitivity of
20 or less.
21. A control system for detecting and reducing fluid leaks along a
seal between a moving fabric web and a web treatment chamber,
wherein the web treatment chamber comprises a pressurized plenum
for applying a fluid at a pressure greater than the ambient
pressure to a surface of the moving fabric web to directly contact
the moving fabric web, a seal between the plenum and the moving
fabric web, and an opposing chamber for removing the applied fluid
from the pressurized plenum, the control system comprising: (a) a
leak detector mounted near the seal, adapted to produce a signal to
indicate the presence and location of a fluid leak between the
moving fabric web and the seal; and (b) localized leak reduction
means responsive to the signal produced by the leak detector.
22. The control system of claim 21, having a Local Sensitivity of
20 or less.
23. The control system of claim 21, wherein the moving fabric web
moves through the web treatment chamber while in contact with at
least one additional fabric web.
24. The control system of claim 21, wherein the seal comprises a
friction resistant material selected from at least one of Teflon, a
fluoropolymer, a ceramic, and a material comprising a surface
having at least one of a nitride, carburized steel, diamond, and a
plasma-deposited agent.
25. The control system of claim 21, wherein the seals are
cooled.
26. The control system of claim 21, wherein the seals are
lubricated with lubrication means.
Description
BACKGROUND OF THE INVENTION
Many devices exist for performing an operation on a moving web
wherein a gas or gas pressure differential is applied. For example,
in the art of papermaking, a wet or embryonic paper web can be
partially dried or dewatered by means of an applied gas pressure
differential using nozzles, a compressive roll with holes or
grooves for pressurized air, an "air press" or other devices
wherein a gas pressure differential forces air into a web to
displace liquid water and/or to remove water by evaporation. Many
prior systems, particularly those having compressive rolls, impose
high compressive force on the web and are not suitable for many low
density materials such as tissue. Systems of nozzles are typically
inadequate due to the low residence time provided for air
penetration into the web. Nozzle systems also either suffer from
high leakage if the nozzle is not in contact with the web or from
high fabric wear if the fabric wraps the surfaces of the nozzle to
provide some degree of sealing. A fabric wrapping a nozzle with a
small effective radius of curvature is particularly likely to
experience wear problems.
Flat pressurized boxes, such as steam boxes, while capable of good
residence time in some cases, suffer from high leakage from the
sides of the steam chamber. Steam boxes for heating paper webs in
particular have tended to be flat boxes with a finite gap between
the web and the sides of the box. Such gaps or clearances allow
significant volumes of air to enter, in part due to the air
boundary layer traveling with the web. Intentionally bleeding steam
to oppose the boundary layer or using a steam curtain to prevent
entry of the boundary layer is inherently inefficient.
Recognizing the difficulty of providing adequate seals in
pressurized paper drying chambers, some have proposed the use of
high-velocity heated air impingement that relies on the momentum of
the air to push through the web for paper drying without attempting
to use seals. This technique is intended to minimize lateral
migration of the drying air along the surface of the web, thereby
reducing the need for sealing. Even if this method reduces the
lateral flow of air, the extent of treatment is limited by the
brief contact time of the pressurized gas with the web due to the
narrow jets employed. Without suitable seal elements, leakage still
will not be prevented.
Rotary devices, such as cylindrical through dryers and suction
rolls, can be operated to pass air through a fibrous sheet but are
complex and costly devices. Further, the surface of the rotary
device or other supporting surfaces in contact with the web have
significant closed areas where gas flow is blocked, resulting in
nonuniform penetration of the gas through the web.
An excellent system for effective gas treatment of a moving web is
the dewatering system disclosed in commonly owned copending
application Ser. No. 08/961,915 of Hada et al. filed Oct. 31, 1997
and incorporated herein by reference in its entirety. This
application teaches an air press wherein a non-rotating upper
plenum is used to apply pressurized air to a moist paper web while
the web is sandwiched between two pervious fabrics. The pressurized
plenum cooperates with a lower vacuum box on the opposite side of
the sandwiched paper web such that the overall pressure
differential across the web is greater than if the pressurized
plenum were used alone at a predetermined pressure. An important
issue in the operation of an air press is preventing unnecessary
leakage of gas out of the plenum into the surrounding atmosphere.
Hada et al. disclose a set of cross-direction seals (seals running
in the cross-direction) for the leading and trailing edges of the
plenum (the leading edge being closest to the headbox) and a pair
of machine-direction seals running in the machine direction to seal
the side edges of the plenum. Hada et al. also disclose a lever
system for increasing sealing force on the seals responsive to
measurement of air pressure in the plenum. The principle of
operation is that excessive leakage will result in a reduction of
pressure in the plenum, which can then be compensated by increasing
the applied pressure to the systems of seals.
Though capable of opposing leakage and preventing large leaks, such
a system may lead to excess fabric wear, particularly in wide
machines, because sealing is generally performed across the entire
width of the machine, rather than solely in the locations where
leak reduction is needed. Further, use of internal pressure
measurements to detect leak control may lead to some false readings
of leakage when pressure fluctuates for other reasons, such as
changes in web properties or compressor operation or air
temperature. Further still, a single macroscopic measure of
pressure cannot be used to locate specific leaks, only leakage in
general. Therefore, what is lacking and needed is a method and
apparatus for detecting the specific location of leaks and applying
corrective remedies to prevent leakage only at the locations where
leakage is occurring.
SUMMARY OF THE INVENTION
Pressurized or depressurized web treatment chambers for processing
moving webs can operate more efficiently if fluid leaks are
detected and controlled with localized leak detection means and
with localized leak reduction means, wherein the leak reduction
means is operatively responsive to the leak detection means such
that local leaks are effectively sealed or reduced in severity.
In particular, a control method has been discovered for web
treatment systems for moving webs, the treatment system involving
at least one chamber at a pressure substantially different from the
ambient pressure, wherein localized leaks are detected by one or
more leak detectors and wherein the leaks are reduced by
application of pressure reduction means responsive to the one or
more leak detectors. The control method of the present invention
can provide improved means for prevention of leaks in web treatment
systems of all kinds wherein a moving web passes through a
pressurized treatment chamber.
Further, the control system of the present invention can be used to
prevent leakage of chemicals from a web treatment chamber or to
prevent excess infusion of atmospheric air or oxygen into web
treatment chamber by means of localized leak or infusion detectors
operatively associated with localized leak reduction means to apply
improved sealing in the localized regions where such action is
needed. Such a system is desirable when the fluid in the web
treatment chamber has a substantially different chemical
composition than the ambient atmosphere and it is desired to
prevent leakage of the treatment fluid into the atmosphere or to
prevent leakage of air into the chamber. Again, it is desirable to
maintain effective seals across substantial distances as a web
passes through the seals through a combination of localized leak
detection and reduction, rather than subjecting the entire
apparatus or entire extent of the web and the seals to increased
clamping pressures. As used herein, the term "leak" encompasses
both the escape of fluid from within the chamber (e.g., the escape
of pressurized air from an air press) and the infusion of fluid
into the chamber (e.g., infusion of the atmosphere into a low
pressure treatment chamber).
Cross-directional flexible seals with leakage control according to
the present invention are desirable for the entrances and exits to
enclosed pressurized web treatment chambers, such as steam heating
chambers, while machine-direction edge seals and a corresponding
control system are desirable for other web treatment devices.
Hence, in one aspect, the present invention resides in a control
system for detecting and reducing fluid leaks along a seal between
a moving web and a web treatment chamber, wherein the web treatment
chamber applies a fluid at a pressure other than the ambient
pressure to a surface of the moving web, the control system
comprising: a) a leak detector for indicating the presence and
location of a fluid leak between the moving web and the seal; and
b) localized leak reduction means responsive to the localized leak
detector means.
In another aspect, the invention resides in a method for reducing
leaks in a pressurized web treatment system for treating a moving
web with a pressurized fluid, the web treatment system comprising a
pressurized chamber, and a seal between the web and the chamber,
comprising: a) detecting a leak along the seal, the leak having an
estimated severity above a predetermined minimum value, b)
identifying the approximate location of the leak; c) generating a
signal indicative of the approximate location of the leak; and d)
increasing local sealing pressure above a predetermined minimum
along the seal in the approximate location of the leak responsive
to the signal, such that leakage is reduced.
The above method can further comprise the step of incrementally
reducing the local sealing pressure in the region where sealing
pressure was increased until leakage in said region begins to
increase, then increasing the sealing pressure again slightly to a
level before increased leakage was detected, whereby excessive
sealing pressures are avoided when not needed to reduce
leakage.
In another aspect, the invention resides in a pressurized web
treatment system for applying a pressurized fluid from a fluid
source to a moving web while dynamically reducing fluid leaks to
the atmosphere, comprising: a) a web treatment chamber comprising
chamber walls that define an interior plenum, a fluid inlet for
receiving pressurized fluid from a fluid source, an opening for
applying pressurized fluid to a moving web, a leading edge and a
trailing edge both extending in the cross direction, opposing side
edges extending in the machine direction, and a flexible seal
assembly along at least one of the leading edge, the trailing edge,
and the side edges, for preventing leakage of the pressurized
fluid, the seal assembly comprising a first seal head in contact
with the web treatment chamber and an opposing second seal head
such that the web passes between the first and second seal heads
and wherein one of the first and second seal heads is urged toward
the other of the first and second seal heads with a sealing force;
and b) a control system for reducing fluid leaks along the seal
assembly comprising a leak detector for identifying the presence
and location of a fluid leak between the moving web and the seal
assembly, and localized leak reduction means responsive to the leak
detector, wherein the localized leak reduction means comprises a
force generator for variably adjusting the sealing pressure along
the length of the seal assembly to reduce leakage in the vicinity
of the fluid leak as identified by the leak detector.
In yet another aspect, the invention resides in a treatment system
for a moving web with improved leakage control, the web having a
first surface and a second surface, comprising: a) a chamber
comprising a plenum for pressurized fluid in fluid communication
with the web, the chamber having at least one edge along which the
web travels into or out of the chamber; b) a flexible seal assembly
in contact with said at least one edge for preventing leakage of
pressurized fluid from the treatment system; c) a leak detector
responsive to fluid leaks along the seal such that the approximate
location of fluid leaks can be identified; and d) localized leak
reduction means along the seal assembly cooperatively associated
with the leak detector such that increased sealing force is applied
where leaks occur.
In yet another aspect, the invention resides in an air press for
dewatering a moving web having improved CD control of leakage,
comprising: a) an air press having at a pressurized gas chamber and
least one CD seal element; b) a localized leak detector external to
the pressurized gas chamber; and c) a localized force generator to
increase the pressure on the seal, the force generator being
cooperatively associated with the leak detector.
Chambers that treat moving webs at pressure other than ambient
pressure and particularly at elevated pressure can be generally
described, in the context of the present invention, as stationary
or non-rotary plenums having a gas inlet to provide a treatment gas
or vapor which can contact the web. Contact of the gas with the web
is typically by means of the gas flowing through an opening or
multiple openings in a treatment face of the chamber that conducts
fluid from the plenum to the moving web. The treatment face may be
substantially flat or curved. Desirably, it is non-rotary (i.e., it
does not rotate continuously during use as does a rotating roll)
and substantially static or stationary. Desirably, the web passes
through the treatment chamber in a substantially flat form and
particularly with a radius of curvature of greater than 30 inches
and more particularly with a radius of curvature of greater than
about 60 inches.
In many embodiments, the treatment gas in intended to at least
partially pass through the thickness of the web, though for steam
heating and treatment with reactive chemicals it is not necessary
for the gas or vapor to fully pass through the web. When the
leakage through open gaps at the entrance, exit, or sides is
unacceptable, sealing at any line or region of potential leakage
can be provided by placing upper and lower seal elements
respectively above and beneath the moving web.
The seal elements are desirably movable or flexible such that they
can be brought into contact with the web or with the fabric, wire,
or belt on which the web may reside. For example, for treatment of
strong movable webs such as a moving textile web, there may be no
need for a supporting wire or fabric and the seals may directly
contact the moving web. In other cases, the web may require the
support a fabric, wire, or belt, such that one seal element
contacts the supporting fabric, wire, or belt, while the other
opposing seal element contacts the moving web directly. For weaker
or more easily damaged materials such as a moist paper web, direct
contact with a seal element, particularly a stationary seal
element, could result in damage to the web. Thus, it is desirable
that certain weak webs such as moist paper webs be sandwiched
between two moving fabrics, wires, or belts, to protect the web
from direct contact with seal elements. In any case, the
combination of the web and any adjacent fabrics, belts, or wires
passes through opposing upper and lower seal elements that extend
across the leakage zone (e.g., across the cross-direction width of
the web for a CD seal element or along the length of the treatment
chamber for an MD seal element) and that prevent excess leakage
from the pressurized treatment chamber.
For the purposes of the present invention, at least one of the
opposing seal elements along a sealing zone is locally deformable,
flexible, or locally movable, such that the seal element can
respond to an increase in a localized driving force to
preferentially adjust the gap between the opposing seal elements in
the region of the locally applied force. Similarly, the seal
element can respond to the urging or biasing of an actuator or to a
change in the position of an actuator or position element attached
to or in contact with the seal element to preferentially move the
seal element toward and/or away from the web only in the region of
the leak. Thus, the sealing means for a treatment chamber comprise
a deformable, flexible, or locally movable seal element responsive
to locally adjustable force generators or position controllers or
means therefor.
Deformable seal elements comprise those of the previously
referenced Hada et al. patent application. Seal elements can be a
single strip or beam of flexible material such as rubber, Teflon
(duPont de Nemours & Co. Inc., Wilmington, Del.) and related
fluoropolymers, polyethylene or polypropylene, or the like, or thin
metallic beams, rods, or shells capable of suitably flexible
deformation under application of force to serve as a sealing
element. In one embodiment, the seal element comprises a series of
slidable sections joined together but capable or independent or
substantial independent deformation or positioning in the sealing
direction (i.e., the direction normal to the axis of the seal zone
and substantially normal to the moving web in the area being
sealed). For example, slidable seal sections can be discrete
sections that are interlocked mechanically, for example by a
dovetail geometric shape the prevents adjacent sections from
separating but permits relative motion in the sealing direction.
Slidable elements also can be individually mounted on rods or
bearing elements to prevent lateral motion while permitting motion
in the sealing direction. Useful support elements for a deformable
seal element include interlocked, slidably movable units driven by
local actuators or pistons; flexible solid or hollow beams; or the
like.
Useful means for applying local sealing force include those systems
for adjusting flexible elements known in the art of crepe blade
control in tissue making, in the art of slice lip control for
headboxes in papermaking, and in the art of press nip control in
elongated nips or extended nips known in the art of wet pressing
for papermaking. As is known in these and other arts, a wide
variety of force generators can be used to drive, bend, flex, move,
or reposition a beam, a portion of a beam, or a slidable section in
a beam. The beam supporting or holding the seal elements should be
deformable or locally movable to permit a force generation means to
adjust the shape or position of the beam locally to enable improved
local sealing upon application of appropriate force. The
deformation or profile of the seal element is determined by the
profile of force applied to it or by the action of position
adjustment means that determine the position or displacement of
structural elements in contact with the seal element.
Locally adjustable force generators or seal element positioners are
used to locally control the sealing effect of the seal element to
eliminate leakage where needed. A force generator or a seal element
positioner such as a position actuator is locally adjustable if
there are multiple regions extending across the zone being sealed
where the applied force or position of a member can be adjusted to
provide a degree of profiling. There are suitably at least two
separately adjustable force generators or seal element positioners,
but desirably there are at least three and specifically at least
five, more specifically at least 8, and more specifically at least
10 separately adjustable force generators or seal element
positioning means.
Examples of force generation means suitable for applying variable
local force to a seal element include thermal expanding rods,
thermal expanding beam elements, thermal hydraulic actuators,
mechanical actuators, electric motors, piezoelectric elements,
single chamber or multiple chambered air bags, gas cylinders,
pneumatic pistons, hydraulic pistons, thermoelectric actuators,
mechanical screws, gear assemblies, pulley assemblies, lever and
fulcrum assemblies, screw and jack assemblies, adjustable spring
assemblies, magnetic force generation systems, or the like. Motors
can also be used, such as electric or combustion-driven motors
adapted for applying torque or force, particularly when the motor
is only required to run momentarily to jog an element into a
suitable position, wherein the element can be locked into place by
a ratchet and pawl or other means. An example of force generation
means coupled to a deformable element is the hydraulically loaded
shoe in a typical extended nip or elongated nip press, such as that
disclosed by Holopainen in U.S. Pat. No. 5,620,566, issued Apr. 15,
1997, incorporated herein by reference. Holopainen teaches a
cross-direction support shoe cooperating with a circular shell
serving as a press roll. The support shoe is movably connected to a
seat, and between the seat and support shoe are a series of sealed
chambers that can receive pressurized fluid. By varying the
pressure in each of the chambers, the force applied to the support
shoe can be locally varied. The support shoe can be a deformable
material to respond more fully to the force profile provided by the
variable pressure in the sealed chambers, thus providing a degree
of pressure profiling applied to a press nip. More generally, for
the present invention, a seat can cooperate with a deformable head
via variable pressure or force generation means therebetween to
provide a pressure profile to the deformable head, the head being
either attached to or cooperating with a seal element. In this
case, the portion of the seal element contacting the web or wire
may be rigid or deformable, for it is the underlying movable head
that is deformable to achieve profiling.
Seal element positioning means can comprise all the previously
mentioned force means adapted to move one body relative to another
by overcoming a force. Other means for adjusting the position of
one body relative to another may be used, including electromotive
systems, magnetic levitation, rack and pinion systems, and the use
of positioning elements slidably mounted on bearings or rods that
can be moved into a desired position.
The deformable or movable seal elements are deformed or moved
locally upon application of appropriate force in response to a
signal or information provided by local leak detection means. Thus,
if local leak detection means indicate that excess gas leakage is
occurring in the central portion of a seal, local sealing force in
the central portion of the seal would be increased to reduce
leakage in that region.
Without wishing to be limited by specific examples, illustrative
leak detectors suitable for the present invention include but are
not limited to the following:
1. Acoustic sensors such as microphones to detect the presence of
leaks based on the sound emitted. An array of microphones or
transducers, either sonic, ultrasonic, or subsonic, can be mounted
on the plenum, adjacent the plenum, remote from the plenum, or in
acoustic communication with the plenum, such that the sensors
respond to sound waves created by the dynamics of the leaking
stream. In many cases, acoustic sensors covering a frequency of
about 1000 Hz to 15,000 Hz will be suitable. Since important
information about the size and intensity of the leak can be
extracted from the combination of sound intensity and its frequency
range or power spectrum, it is desired in some applications that
both frequency and intensity information be obtained.
2. Vibration detection systems such as piezoelectric devices or
accelerometers responsive to localized motion of solid surfaces on
or adjacent to the treatment chamber that can give non-baseline
readings in the presence of leaks. Laser-based Doppler anemometers,
speckle interferometers, or the like can also be used to assess
vibration of a surface.
3. Thermal flow detection means based on the increased heat
transfer that occurs in higher velocity flow or based on a
temperature difference between the ambient fluid and the
pressurized or depressurized fluid in the plenum. In the presence
of increased velocity flow, the increased heat transfer coefficient
can be sensed with heat flux detectors or hot wire anemometers.
Psychrometers, wet bulb thermometers, wetted surfaces, and other
devices can indicate the presence of increased velocity gas flow
due to the improved evaporative transport or cooling that occurs.
When fluid at an elevated or depressed temperature relative to the
ambient atmosphere escapes from the plenum, it will result in flows
having different temperatures which can be measured by
thermometers, thermocouples, thermistors, infrared detectors,
liquid crystal thermal displays, other known temperature sensors,
thermography with IR-sensitive cameras, or the like. Likewise, if
leakage from the atmosphere into a depressurized plenum occurs, the
increased heat transfer caused by the in-rushing air or the local
temperature changes caused by the atmosphere can be detected with
temperature or heat flux measurement means, preferably mounted
inside the plenum near the region of potential leakage or mounted
on or in the seal elements. Thermal flow detection means can also
be responsive to the temperature change that can occur as a
pressurized gas passes through a narrow orifice, such as the
Joule-Thompson effect.
4. Optical sensors that respond to the gap thickness between
opposing seal surfaces to detect changes in light transmission
through the edges of the pressurized plenum, particularly in
conjunction with suitable light sources. For example, a CCD strip
inside a plenum could respond to light from a bright line of lights
or a fluorescent tube outside the plenum with suitable light guides
and optics to identify the location of the light leak.
5. Chemical sensors, particularly gas sensors for a particular
chemical species, that respond to a major or trace component in the
treatment gas which may leak into the ambient atmosphere and be
detected, or that respond to oxygen or other components of air when
entry of the atmosphere into a treatment chamber is to be
detected.
6. Gap size measuring devices to directly measure the gap between
two opposing seal surfaces or between a seal and a web or fabric,
wherein gap size is maintained to a preset value or adjusted in
response to leakage detection. Eddy current sensors can also be
used to measure the distance between metal components inside two
opposing sealing surfaces to assist in regulating and controlling
gap thickness at the seals. Gap size can be correlated to leakage
or leakage tendency.
7. Mechanical indicators of local flow such as a series of vanes or
other rotating devices capable of moving in response to the
presence of a local leak, or strips of flexible material such as
strings or cloth secured at at least one end and unsecured over a
portion of the length of the article such that waving or flapping
is possible in response to a leak, to provide a visual cue that
leakage is occurring. Flaps, ribbons, and other materials movable
in response to air flow can be used.
8. Gas flow or velocity measurement devices such as laser
anemometry, hot film or hot wire anemometers, other optical
velocimeters, small turbine or vane anemometers, or other such
devices to measure the presence of leaks directly in the location
of a potential leak zone. In the case of laser Doppler anemometry,
the optics could be scanned to move the focal point or measurement
volume of the device along a finite zone where leakage may occur.
Alternatively, the entire anemometer could be physically scanned,
or multiple lasers and optical systems could be used to examine
multiple regions.
9. Flow visualization means can be applied to make a local leak
visible. For example, a film of surfactant-treated liquid applied
near leakage zones could result in a bubble or a visible stream of
bubbles near the leak. Likewise, dust, particulates, entrained
droplets, aerosols, or other non-gaseous material near the zone of
leakage or periodically applied near the zone of potential leakage
can provide a visual cue of leakage due to the plumes or visible
flow streams created by entrainment or disruption of the materials.
The escaping fluid itself may be visible as it escapes from the
plenum or may be made visible by means of adding, if only at
discrete intervals in time, an amount of a particulate or
condensable stream such as steam or an aerosol such as fog or oil
droplets or an entrained solid phase such as TiO.sub.2 or dust. The
visible or visualizable escaping (or, for depressurized system,
in-rushing) flow can be detected in any way known in the art, such
as by image analysis of CCD camera images. The visible stream can
also be sensed optically by the changed intensity of a light beam
passing across the potential leakage zone as sensed by a
photodetector or optical eye.
For detection of leaks from a pressurized chamber, leak detector
sensors or systems will generally be external to the pressurized
plenum (though some optical and flow-based detection means may
require or be successful with internal probes or sensing devices
mounted inside the plenum). For detection of leaks of air or other
gases into a depressurized plenum, leak detection sensors can
typically be mounted inside the plenum, particularly for oxygen
sensors detecting air entry into a chamber.
In a typical embodiment, a moving web is treated in a pressurized
chamber. The web may be a web of textile; a woven or nonwoven
fabric; a web of papermaking fibers; a polymeric film such as an
apertured film; a film undergoing aperturing; an impervious film
being treated on one surface at elevated fluid pressure; a metallic
foil or sheet; a mat of vegetable matter; a thin wood composite; or
the like.
In one application, the moving web comprises activated carbon
fibers or a precursor for preparation of activated carbon fabrics.
Particularly, the web can be a mat of woven or nonwoven fiberglass
or other temperature-resistant inert web impregnated with a
phenolic resin preferably further comprising a crosslinking agent
such that the resin can be charred while on the inert web to form a
carbonaceous coating on the inert web. The charred web can then be
treated in a heated gas treatment chamber to activate the carbon
and provide desired surface chemistry. Gases such as hydrochloric
acid, ammonia, ozone, and other compounds can be used. Acidic
groups can be added to the surface of the activated carbon by
treating the fibers at elevated temperature in the presence of
steam, carbon dioxide, nitric acid, or the like. Basic groups,
useful for absorbing acidic compounds such as HCl, can be
introduced by treatment with ammonia at elevated temperatures or by
other treatments known in the art. Suitable fibers and fiber
treatment methods include those disclosed in PCT patent
application, "Coated Absorbent Fibers," by James Economy and
Michael Daley of the University of Illinois, published as WO
96/38232, Dec. 5, 1996, and on the Univ. of Illinois Web site at
"http://www.students.uiuc.edu/.about.ahall/activated carbon
fabrics.html" as of Jun. 1, 1998, which discloses a variety of gas
treatments at elevated temperature to activate the fibers and
control the surface chemistry. The gases should be at a pressure
above atmospheric pressure to resist entry of air and should pass
completely through the charred web to treat the carbon. Seals are
needed for the web as it enters and leaves the heated gas treatment
chamber to prevent excess consumption of treatment gas and to
prevent oxygen entry. The seals and control system of the present
invention can be used for treatment of such webs for the production
of activated carbon fabrics. Such activated carbon fabrics are
useful for odor control and particularly for incorporation into an
absorbent article, for filtration of gases, for use as face masks
for medical purposes, for absorption of chemical warfare agents, or
the like.
The seal control system of the present invention can also be used
in steam boxes for heating and drying of paper webs and textiles,
for displacement dewatering of wet webs wherein gas displaces
liquid water, for pressurized units in which heated gas is used to
create apertures in polymeric films for subsequent use as cover
materials in absorbent articles, for particle entrainment in
nonwoven and woven webs, for ozonation of textile, paper, and other
webs, including disinfectant treatments; or the like.
The control method of the present invention can provide improved
means for prevention of leaks in web treatment systems of all kinds
wherein a moving web passes through a pressurized treatment
chamber. For example, the leakage control system of the present
invention is not only suitable for pressurized treatment chambers
in which gas passes through a web, but for pressurized treatment
chambers where gas at elevated pressure is used to react with or
heat a web, particularly for drying. Several examples of a steam
treatment chamber for drying a web are found in "Condebelt" drying
systems, wherein a paper web is heated on one side by a metal band
and the web is cooled on the other side, as disclosed in the
following patents: U.S. Pat. No. 5,594,997 issued Jan. 21, 1997 to
Lehtinen; U.S. Pat. No. 4,899,461 issued Feb. 13, 1990 to Lehtinen;
U.S. Pat. No. 5,594,996 issued Jan. 21, 1997 to Haavisto; and U.S.
Pat. No. 4,958,444 issued Sep. 25, 1990 to Rautakorpi et al.; all
of which are incorporated herein by reference. Cross-directional
flexible seals with leakage control according to the present
invention are desirable for the entrances and exits to pressurized
web treatment chambers, such as the steam-heated chambers of
Haavisto, while machine-direction edge seals and a corresponding
control system are desirable for the apparatus disclosed by
Lehtinen.
The disclosed control system may also be used with single CD seal
elements, meaning that the treatment chamber only has one side with
a CD seal. The need for a single seal can arise in a variety of
cases where a roll of a web such as a textile resides in a
pressurized chamber from which the web is unwound and withdrawn
without completely relieving the pressure in the chamber. The
objective, then, is to maintain a CD seal to reduce pressure loss
from the chamber. The need for only one CD seal can arise when a
web is formed or created under pressurized conditions and is
removed from a reaction chamber without the need for a
corresponding seal on the web going into the chamber because the
web as such does not go into the chamber but is formed therein.
Alternatively, some pressurized treatments may have two CD seals
but only one seal requires improved sealing or CD seal control.
Likewise, a treatment may have more than two CD seal sections
having CD control.
The principles of the present invention extend not only to CD leak
control but also to MD leak control. Specifically, the seal
extending along the side edges of a pressurized web treatment
device may also be subject to leakage in particular locations and
may also benefit from localized leakage detection and control.
Certainly CD seals tend to have greater length than MD seals in
many web handling situations because there is a trend to make
machines increasingly wider. Nevertheless, the finite extent of MD
seals in web treatment devices also gives rise to nonuniform
leakage spots and makes it advantageous to provide selective local
adjustment of sealing force on or the position of seal elements to
prevent leakage without excessive wear of seal components, fabrics,
or other elements due to unnecessary clamping or excessively high
force or friction.
The MD seals can be flexible lips that engage any support fabrics
for the moving web along the extreme sides of the fabrics, with air
hoses, air bags, solenoids, hydraulic cylinders, pneumatic
cylinders, screws, and other known force generating means being
used to provide the possibility of profiling in sealing force along
the extent of the MD seal. As with CD seals, leakage detection
means can identify the location of leaks and send a signal to the
force generating means to adjust the sealing pressure in the region
of the leakage. The air press system of Hada et al. in U.S.
application Ser. No. 08/961,915, filed Oct. 31, 1997 provides
examples of MD seals as well as CD seals.
One aspect of the present invention concerns an air press for
noncompressively dewatering the wet web. The air press is disclosed
in the commonly owned copending application of Hada et al.,
previously incorporated by reference. The air press is a
particularly desirable apparatus for dewatering an uncreped
throughdried web to about 30 percent consistency or greater prior
to a differential speed transfer. While pressurized fluid jets in
combination with a vacuum device have previously been discussed in
the patent literature, such devices have not been widely used in
tissue manufacturing. A disincentive to using such equipment is
believed to be due to the difficulties of actual implementation,
including pressurized fluid leaks. The air press of Hada et al.
overcomes many prior objections to such a process, and coupled now
with the leakage control system of the present invention, offers
significant improvements in the ability to dewater a sheet
effectively either prior to through drying or as an enhancement of
tissue production with a Yankee dryer. In the latter case, improved
tissue dried by a Yankee dryer can be made by imparting texture and
bulk to the web with sculpted or contoured fabrics such as the
sculpted TAD fabrics of Chiu et al. in U.S. Pat. No. 5,429,686,
issued Jul. 4, 1995 and incorporated herein by reference, but the
texturized tissue web will have less contact with the Yankee unless
pressed so hard as to lose the benefits of the texture imparted by
the fabric. Less contact with the Yankee reduces drying rates, so
additional drying is needed prior to the Yankee for effective sheet
molding and structuring. The air press provides a practical
apparatus for dewatering a wet web to consistency levels not
previously thought possible at industrially useful speeds without
thermal dewatering.
In one embodiment, an air press for dewatering a wet web comprises:
support fabrics adapted to sandwich the wet web therebetween and
transport the wet web through the air press; a first dewatering
device comprising a pair of cross-machine direction sealing members
including sealing blades; a second dewatering device comprising a
cross-machine direction sealing member formed of a deformable
material, the first and second dewatering devices moveable relative
to one another and adapted to assume an operating position in which
the first and second dewatering devices are operatively associated
with one another and at least one sealing blade impinges upon the
support fabrics and is opposed on the other side of the support
fabrics by the sealing member formed of deformable material; and
wherein one of the first and second dewatering devices comprises an
air plenum operatively connected to a source of pressurized fluid
and the other comprises a collection device operatively connected
to a vacuum source.
In another embodiment, an air press for dewatering a wet web
according to the present invention comprises: support fabrics
adapted to sandwich the wet web therebetween and transport the wet
web through the air press; an air plenum positioned on one side of
the wet web and operatively connected to a source of pressurized
fluid, the air plenum comprising a profitable or segmented sealing
assembly that is adapted to move at each segment or section between
an operating position and a retracted position, the sealing
assembly comprising a pair of machine direction sealing members and
a pair of cross-machine direction sealing members that form an
integral seal with the wet web when the sealing assembly is in the
operating position; a collection device positioned on the opposite
side of the wet web and operatively associated with the air plenum,
the collection device defining therein sealing slots that extend
across the width of the wet web and also defining therein a central
passageway disposed between the sealing slots and adapted to
receive pressurized fluid from the air plenum and water from the
wet web, and means for moving the machine direction sealing members
into and out of contact with one of the support fabrics, the
machine direction sealing members forming a seal when the sealing
assembly is in the operating position.
The air press is able to dewater the wet web to very high
consistencies due in large part to the high pressure differential
established across the web and the resulting air flow through the
web. In particular embodiments, for example, the air press can
increase the consistency of the wet web by about 3 percent or
greater, particularly about 5 percent or greater, such as from
about 5 to about 20 percent, more particularly about 7 percent or
greater, and more particularly still about 7 percent or greater,
such as from about 7 to 20 percent. Thus, the consistency of the
wet web upon exiting the air press may be about 25 percent or
greater, about 26 percent or greater, about 27 percent or greater,
about 28 percent or greater, about 29 percent or greater, and is
desirably about 30 percent or greater, particularly about 31
percent or greater, more particularly about 32 percent or greater,
such as from about 32 to about 42 percent, more particularly about
33 percent or greater, even more particularly about 34 percent or
greater, such as from about 34 to about 42 percent, and still more
particularly about 35 percent or greater.
The air press is able to achieve these consistency levels while the
machine is operating at industrially useful speeds. As used herein,
"high-speed operation" or "industrially useful speed" for a tissue
machine refers to a machine speed at least as great as any one of
the following values or ranges, in feet per minute: 1,000; 1,500;
2,000; 2,500; 3,000; 3,500; 4,000; 4,500; 5,000, 5,500; 6,000;
6,500; 7,000; 8,000; 9,000; 10,000, and a range having an upper and
a lower limit of any of the above listed values. Optional steam
showers or the like may be employed before the air press to
increase the post air press consistency and/or to modify the
cross-machine direction moisture profile of the web. Furthermore,
higher consistencies may be achieved when machine speeds are
relatively low and the dwell time in the air press in higher.
The pressure differential across the wet web provided by the air
press may be about 25 inches of mercury or greater, such as from
about 25 to about 120 inches of mercury, particularly about 35
inches of mercury or greater, such as from about 35 to about 60
inches of mercury, and more particularly from about 40 to about 50
inches of mercury. This may be achieved in part by an air plenum of
the air press maintaining a fluid pressure on one side of the wet
web of greater than 0 to about 60 pounds per square inch gauge
(psig), particularly greater than 0 to about 30 psig, more
particularly about 5 psig or greater, such as about 5 to about 30
psig, and more particularly still from about 5 to about 20 psig.
The collection device of the air press desirably functions as a
vacuum box operating at 0 to about 29 inches of mercury vacuum,
particularly 0 to about 25 inches of mercury vacuum, particularly
greater than 0 to about 25 inches of mercury vacuum, and more
particularly from about 10 to about 20 inches of mercury vacuum,
such as about 15 inches of mercury vacuum. Both pressure levels
within both the air plenum and the collection device are desirably
monitored and controlled to predetermined levels.
The collection device desirably but not necessarily forms an
integral seal with the air plenum and draws a vacuum to facilitate
its function as a collection device for air and liquid. The terms
"integral seal" and "integrally sealed" are used herein to refer
to: the relationship between the air plenum and the wet web where
the air plenum is operatively associated and in indirect contact
with the web such that about 70 percent or greater of the air fed
to the air plenum flows through the web when the air plenum is
operated at a pressure differential across the web of about 30
inches of mercury or greater; and the relationship between the air
plenum and the collection device where the air plenum is
operatively associated and in indirect contact with the web and the
collection device such that about 70 percent or greater of the air
fed to the air plenum flows through the web into the collection
device when the air plenum and collection device are operated at a
pressure differential across the web of about 30 inches of mercury
or greater.
Significantly, the pressurized fluid used in the air press is
sealed from ambient air to create a substantial air flow through
the web, which results in the tremendous dewatering capability of
the air press. The flow of pressurized fluid through the air press
is suitably from about 5 to about 500 standard cubic feet per
minute (SCFM) per square inch of open area, particularly about 10
SCFM per square inch of open area or greater, such as from about 10
to about 200 SCFM per square inch of open area, and more
particularly about 40 SCFM per square inch of open area or greater,
such as from about 40 to about 120 SCFM per square inch of open
area. Desirably, 70 percent or greater, particularly 80 percent or
greater, and more particularly 90 percent or greater, of the
pressurized fluid supplied to the air plenum is drawn through the
wet web into the vacuum box. For purposes of the present invention,
the term "standard cubic feet per minute" means cubic feet per
minute measured at 14.7 pounds per square inch absolute and 60
degrees Fahrenheit (.degree. F.).
The terms "air" and "pressurized fluid" are used interchangeably
herein to refer to any gaseous substance used in the air press to
dewater the web. The gaseous substance suitably comprises air,
steam or the like. Desirably, the pressurized fluid comprises air
at ambient temperature, or air heated only by the process of
pressurization to a temperature of about 300.degree. F. or less,
more particularly about 150.degree. F. or less.
In an alternative embodiment, a device for dewatering a wet web
traveling in a machine direction, comprises: a frame structure;
support fabrics adapted to sandwich the wet web therebetween; an
air press comprising an air plenum and a collection device
positioned on opposite sides of the wet web and support fabrics,
the air plenum and collection device operatively associated with
one another and adapted to establish a flow of pressurized fluid
through the wet web, the air plenum comprising: stationary
components mounted on the frame structure; a profitable sealing
assembly that is adapted to move relative to the stationary
components between an operating position and a retracted position
with variation in position of segments or sections along the
sealing assembly providing a degree of independent control over
each segment or section. The sealing assembly comprises a pair of
optionally profitable machine direction sealing members and a pair
of profitable cross-machine direction sealing members that together
form an integral seal with the wet web when the sealing assembly is
in the operating position; means for moving the cross-machine
direction sealing members generally perpendicular to a plane
containing the wet web and into and out of contact with one of the
support fabrics; means for moving the machine direction sealing
members generally perpendicular to the plane containing the wet web
and into and out of contact with one of the support fabrics; and
means for moving the machine direction sealing members generally
parallel to the plane containing the wet web and generally
perpendicular to the machine direction.
In another alternative embodiment, a device for dewatering a wet
web traveling in a machine direction, comprises: a frame structure;
support fabrics adapted to sandwich the wet web therebetween; an
air press comprising an air plenum and a collection device
positioned on opposite sides of the wet web and support fabrics,
the air plenum and collection device operatively associated with
one another and adapted to establish a flow of pressurized fluid
through the wet web, the air plenum comprising: stationary
components mounted on the frame structure and defining a loading
surface generally parallel to a plane containing the wet web; a
sealing assembly that is adapted to move relative to the stationary
components between an operating position in which the sealing
assembly forms an integral seal with the wet web and a retracted
position, the sealing assembly defining a control surface generally
parallel to the plane containing the wet web and adapted to contact
the loading surface; and means for moving the sealing assembly
generally perpendicular to the plane containing the wet web,
wherein contact between the control surface and the loading surface
interrupts movement of the sealing assembly toward the wet web when
the sealing assembly reaches the operating position.
The air press may use internal surfaces that are normal to the
loading direction to completely isolate the loading force from the
air plenum pressure. Thus, the loading force can be maintained at a
constant value to provide a proper seal despite the air plenum
pressure varying from zero to maximum pressure. Accordingly, the
loading force does not have to be adjusted in response to pressure
changes within the air press.
Definition of Terms and Test Procedures
As used herein, "fluid" refers to non-solid matter, specifically
liquids or gases. Though gas is most commonly used in pressurized
web treatment chambers, liquids can also be applied. Liquids that
could be used according to the present invention include water,
resins to make impregnated paper, dyes, surface chemistry modifying
solutions, supercritical fluids (classifiable as either a liquid or
a gas), solvents for removing undesired components, or the
like.
As used herein, "gas" refers to a chemical composition which is not
in a liquid or solid state, but is gaseous. Exemplary gases of use
in the present invention include air, steam, nitrogen, oxygen,
ozone, chlorine, bromine, and other halogens, acid vapors such as
HCI or sulfuric acid fumes, ammonia and nitrogenated compounds,
chlorinated species such as bleaching agents or dry cleaning
compounds, solvent vapors, formaldeyde and other crosslinking
agents, alcohols, or the like, either as pure components or in
mixtures.
As used herein, "vapor" refers to a readily condensable gas or the
gases resulting from evaporation or boiling of a substance, with
examples including steam, aliphatic fumes, many acid fumes, fumes
of many heavy metal organic compounds in the gaseous state,
particularly titanium and osmium compounds, sublimed material, or
the like. The gases or vapors used to treat webs may also carry
entrained or suspended liquid or solid materials such as
superabsorbent particles; pH modifying agents or buffer compounds,
activated carbon particles or fibers; synthetic or natural
polymeric fibers or particulates; oils and emollients; dust; fume
particles; baking powder; skin wellness agents such as zinc oxide
or dimethicone; surfactants; bleaching agents; colors, dyes, and
pigments; inorganic fillers such as calcium carbonate, titanium
dioxide, chalk, talcum; or the like.
As used herein, "cross direction" (CD) refers to the direction
substantially normal to the machine direction (the direction of
movement) of a moving web. A seal element is said to run
substantially in the cross-direction of the web if it extends
across a greater distance normal to the machine direction than it
extends in the machine direction. Desirably, the CD seal extends
substantially across all of the width of a web.
As used herein, "Local Sensitivity" is the percentage of the linear
extent of a sealed region that is occupied on the average by a
separately controllable force generator or position controlling
device. For example, a spaced apart linear array of 5 independently
adjustable pistons or pressurized hose segments along a
cross-direction seal could apply CD force profiling across the
sealing zone with a Local Sensitivity of 20%.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of the cross-section of an air press system
showing a seal assembly and a microphone system for leak
detection.
FIG. 2 shows one embodiment of a seal head used on one side of the
web for a CD seal.
FIG. 3 shows a seal head and a support plate with pressurization
means for controlling the force applied to the seal head.
FIG. 4 shows an enlarged portion of the seal head and support plate
of FIG. 3 in the plane of line 44 illustrating the isolated
pressurization chambers in the cross-direction.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows one embodiment of an air press 1 for dewatering or
otherwise treating a web 2 such as a paper web or other fibrous
web. The web 2 can reside on a lower fabric 3 and can reside
adjacent to an upper fabric 5. In the case of paper, it is
desirable that the web 2 be sandwiched between both a lower fabric
3 and an upper fabric 5 moving at the same velocity as the web,
which moves in the machine direction as indicated by the arrow 35
(from left to right in FIG. 1). The air press comprises an upper
chamber 7 with a conduit 9 to a pressurized air or gas source P.
The chamber walls define an upper plenum 11. The web 2 and any
adjacent fabrics pass beneath the upper air press chamber 7 and
over a support shoe 21 having support elements 25 and gas ports or
vacuum slots 23 through which gas from the plenum can pass.
Desirably, gas passing through the support shoe 21 passes into a
lower plenum 27 in a vacuum box 30 from which it exits the air
press assembly by means of a vacuum pump or other vacuum source V.
Alternatively, the gas can be discharged through the shoe and into
the atmosphere without reliance on a vacuum. The support elements
25 between the gas ports or vacuum slots 23 prevent excessive
deflection of the web and any fabrics under the pressure
differential that exists between the pressurized upper plenum 11
and the lower plenum 27.
To prevent excessive leakage along the cross-direction extent of
the air press, leading and trailing edge seal assemblies 6a and 6b
are provided at the leading and trailing edges of the air press,
respectively. The leading edge seal assembly 6a can be similar to
the trailing edge seal assembly 6b, as is the case in FIG. 1, or
can employ other embodiments of the present invention. Turning
attention to the trailing edge seal assembly 6b as a general
example of one embodiment and as representative also of the leading
edge seal assembly 6a, the seal assembly 6b comprises an upper seal
head 13b which can deflect the web 2 and any adjacent fabrics 3, 5
into a recess 18b formed in a lower seal head 19b. The illustrated
lower seal head 19b comprises first and second seal head members
37b and 39b which define therebetween the recess 18b and a support
plate 29b, which can be a flexible or sectioned plate, a beam, a
series of slidably movable segments, or other structures providing
support and stability to the seal head 19b. Alternatively, the
lower seal head 19b may comprise a deformable, flexible, and/or
wearable portion with the web 2 being deflected toward or into this
portion (not shown). Recess 18b is desirable, particularly for
reducing friction, but is not essential, for the two lower seal
head elements 37b and 39b can be replaced with a single lower seal
head element in line with the upper seal head element 13b such that
a sealing force can be directly transmitted between the opposing
upper and lower seal head elements, at least one of which is
deformable or movable such that a profile in the gap size between
the opposing elements can be achieved and controlled along the
length of the seal assembly 6b.
Support plate 29b can comprise either discrete zones in the
cross-direction or a unitary structure that is flexible or
deformable such that the positions of, or sealing force on, lower
seal head 19b can be varied in the cross-direction by the local
action of a force generation means or seal element positioning
means 60b which cooperates with the base plate 29b and/or the seal
head elements 37b and 39b to control the local sealing pressure or
gap size along the length of the seal assembly 6b. Alternatively,
the lower seal heads 37b and 39b are substantially fixed and the
upper seal head 13b is movable normal to the web 2 via force
generation means or position control means with cross-direction
variability possible to permit control of the sealing force or
relative sealing efficiency of the seal assembly 6b in the
cross-direction.
When the relative positions of the upper seal head 13b and the
lower seal head 19b are improperly adjusted, a gas leak can form
through an escape route 33. This leak can be detected by leak
detection means 31b, depicted in FIG. 1 as a microphone,
representative of a bank of acoustic sensors whose signals can be
analyzed to detect the proximity of the leak 33. The signal from
the leak detection means 31b serves as input 54b to a controller 50
which can provide a signal 58b to force generation means or seal
element positioning means 60b. Thus, elimination or reduction of
the gas leak can be achieved by increasing the sealing force
between the opposing seal heads 13b and 19b by force generation
means 60b, or by adjusting their relative position by seal element
positioning means 60b in the region of the escape route 33, as
opposed to simply increasing the sealing pressure along the entire
CD width of the seal assembly 6b.
Detection of the leak occurring through the escape route 33 can
occur through a variety of leak detection means. FIG. 1 depicts a
microphone 31b, which would be one of multiple microphones or
acoustic sensors mounted near the air press's seal assembly 6b and
spaced apart or distributed in the cross-direction. The sound made
by the escaping gas passing through the escape route 33 can be
detected by the microphone 31b and can also be analyzed for
frequency and intensity information that can indicate the severity
and nature of the leak. Based on analysis of the signal from the
microphone by controller 50, the location of escape route 33 can be
approximately identified. The controller 50 can comprise a
microcomputer, an electronic circuit, or a manually operated
system, to direct, guide, or control the action of the force
generation means or seal element positioning means 60b to reduce
the degree of leakage. Algorithms for computer control of the force
generation means based on input from the leak detector 31b can
readily be devised using techniques known in the art. The
controller 50 directs force generation means or seal element
positioning means to adjust the sealing force of the seal (or the
relative position of the opposing seal heads) in the vicinity of
the escape route 33 until the degree of leakage has been acceptably
reduced. For example, a signal from the controller 50 can direct
pneumatic devices associated with a segmented air hose to increase
the air pressure in the segment associated with the region of
leakage, or a signal from controller 50 can direct mechanical
actuators to apply more or less force to particular segments of the
seal assembly to control leakage. The controller 50 can be
considered part of the leak detector 31b in terms of function but
can have separate electronics or other components. Indeed, the
electronics or other components needed for the simple task of
interpreting the signal from the leak detector can physically
reside within the body of the force generation means 60b or can be
separate.
Secondary information about seal efficiency can also be extracted
from pressure in the upper plenum 11, pressure in the lower plenum
27, gas mass flow rates out of the lower plenum 27 (as detected by
a mass flow meter, for example), and by web properties associated
with gas treatment (e.g., web moisture content and CD uniformity
thereof when the air press is used to dewater a web). This
information can be coupled to the controller 50 for validation or
backup purposes, but information from the local leak detection
means 31b provides critical input for selection of sealing or
positioning strategies to reduce leakage and improve the efficiency
and uniformity of treatment.
Desirably, the upper fabric 5, if used, has high permeability in
the z-direction but has low in-plane permeability in the machine
direction in order to prevent leakage through the fabric in the
machine direction (or in the reverse machine direction). An example
of a web with essentially no in-plane permeability would be a web
made of laminated impervious layers provided with small isolated
z-direction holes or apertures passing directly through the web,
with hole diameters less than the contact length of the fabric
against the upper seal head 13b. The fabrics 3 and 5 should be wear
resistant and generally smooth to reduce friction.
Seal heads 13b, 37b, and 39b generally contact moving surfaces and
may abrade. Therefore, it is desirable that they comprise abrasion
resistant materials having low friction. Teflon and related
fluoropolymers are known for low friction. Other synthetic polymers
and ceramic materials known to offer good wear resistance and low
friction can also be used, possibly with optional surface
treatments such as plasma deposition of diamond or boron nitride
for improved wear or lower friction. Silicon nitride is also known
for excellent wear resistance, as are a variety of ceramic
components and other materials now used in the art of papermaking
for foils that contact moving fabrics. Other materials known in the
art can be used, including metal such as steel with appropriate
surface treatments such as carburization, ceramic deposition,
plasma spray deposition of wear-resistant nitrides, or the like.
Likewise, wear resistant fabrics are desirable to serve as
web-contacting fabrics 3,5.
Desirably, the wearing surfaces of the seal heads 13b, 37b, and 39b
are further provided with lubrication means and/or cooling means
(not shown). A small quantity of water or other liquids suitable
for the particular application may be applied to sealing head by
spray or slot injection or other means just before the point of
wire or fabric contact to reduce friction and also provide
cooling.
FIG. 2 shows the lower seal head 19b of the seal assembly 6b from
FIG. 1, with a support plate 29b and seal head members 37b and 39b.
The seal head members 37b and 39b have an outer surface with a
contact region 44 for contacting a moving web, fabric, or belt. The
seal head 19b permits variable CD control of applied force or of
the position of the seal head members 37b and 39b at various zones
in the cross-direction because the seal head 19b comprises
individually movable segments 42 that are joined together but can
move toward or away from the web to adjust the sealing efficiency
in use. The segments 42 may be mounted on rods or other structures
or may be geometrically connected as by a dovetail assembly to
prevent separation in the cross-direction but to permit slidable
movement normal to the cross-direction toward or away from the
moving web. Force generation means or seal element positioning
means 60b operatively connected to the individual segments 42, as
indicated by lines 62 (which can represent direct or indirect
contact by actuators, pneumatic devices, or other devices) can be
used to adjust the position or applied force for each segment.
Desirably, force generation means 60b act on the underside of the
support plate 29b. The segments 42 of the support plate 29b can be
rigid, and the seal head elements 37b and 39b can be deformable or
rigid or have both rigid and deformable materials combined for
effective sealing. Springs or similar deformable devices may be
used to provide flexibility to segmented seal head elements 37b and
39b, which can comprise, for example, a rigid contacting strip
supported by a spring element.
FIG. 3 shows a cross-section of a seal head 69 which can serve as
an upper or lower seal head, such as seal heads 13b or 19b of FIG.
1, or as seal head element 37b or 39b of FIG. 1, or as a single
section 42 of a seal head 19b in FIG. 2, or as a general seal head
in a seal assembly. The cross-section is taken perpendicular to the
sealing axis. Seal head 69 comprises a sealing member 74 with a
contacting surface 76 for contact with either the moving web or a
moving fabric, belt, or wire. Sealing member 74 can be flexible and
can be abrasion resistant, and can comprise an abrasion resistant
layer of material such as silicon nitride or ceramic connected to a
more flexible material such as plastic. Sealing member 74 is joined
to a movable body 72 which can move relative to a support base or
support element 70. A chamber 80 is defined by the internal walls
of the support base 70 and the movable body 72. Chamber 80 can be
pressurized by injection of fluid such as water, oil, or air
through a fluid port 78 connected to a pressurized fluid source
(not shown). Generally, the fluid for pressurizing chamber 80 is
not associated with the fluid for pressurizing the web treatment
chamber, but is isolated and separate. It can be delivered by means
of hydraulic pistons, gas compressors, pumps, or the like,
operatively associated with the controller (not shown) which
directs the level of pressure to be applied to chamber 80, which
desirably is just one of multiple independently pressurizable
chambers along the length of the seal assembly. Movable body 72 can
be flexible to allow one portion to be locally adjusted relative to
other portions by controlling the internal pressure in discrete
internal chambers 80, or can be segmented to allow independent
application of force or position control of each segment. By
adjusting the pressure in chamber 80, the local sealing force
applied to the sealing member 74 is controlled, or, similarly, the
position of sealing member 74 can be adjusted when it is opposed by
a resisting force from a deformed web, for example.
FIG. 4 shows an enlarged portion of the cross-section view taken in
the plane of line 4--4 in FIG. 3, offering a view normal to the
sealing axis of the seal head 69, which, in this case, is
segmented. FIG. 4 depicts how chamber 80 for one segment of a seal
is isolated from other segments to permit local control of sealing
pressure. In this embodiment where the seal head 69 in FIG. 3
extends in the cross-direction, the view in FIG. 4 is taken in the
machine direction. Chamber 80 between the support base 70 and the
movable body 72 is shown, as is the fluid port 78. Chamber 80 has a
finite extent along the sealing axis and is bound by wall elements
84 and 86 integrally connected respectively to the support base 70
and the movable head 72. Between the adjoining wall elements 84 and
86 is an internal sealing element 90 which separates one
pressurized chamber 80 from the surrounding pressurized chambers,
allowing different sealing pressures to be applied to various
portions of the seal assembly. Sealing element 90 can be an O-ring,
a gasket, a flexible strip, an inflatable member, other mechanical
seals, or can represent any kind of sealing contact between
adjoining wall elements 84 and 86 such that chamber 80 is
substantially independently pressurizable relative to adjoining
chambers. Movable head 72 can move or slide relative to support
base 70, with a wide range of motion made possible by internal
wells 88 which can receive the protruding wall elements 84 and
86.
In FIGS. 3 and 4, the movable head can be a contiguous beam that is
flexible along the sealing axis for localized sealing control, or
can comprise discrete sections that can move independently in the
sealing direction (normal to the web) for fine localized
control.
It will be appreciated that details of the foregoing embodiments,
given for purposes of illustration, are not to be construed as
limiting the scope of this invention. Although only a few exemplary
embodiments of this invention have been described in detail above,
those skilled in the art will readily appreciate that many
modifications are possible in the exemplary embodiments without
materially departing from the novel teachings and advantages of
this invention. Accordingly, all such modifications are intended to
be included within the scope of this invention, which is defined in
the following claims and all equivalents thereto. Further, it is
recognized that many embodiments may be conceived that do not
achieve all of the advantages of some embodiments, particularly of
the preferred embodiments, yet the absence of a particular
advantage shall not be construed to necessarily mean that such an
embodiment is outside the scope of the present invention.
* * * * *
References